A core drill is a drill specifically designed to remove a cylinder of material, much like a hole saw. The material left inside the drill bit is referred to as the core.
Core drills are used for many applications, either where the core needs to be preserved (the drilling apparatus used in obtaining a core sample is often referred to as a corer), or where drilling can be done more rapidly since much less material needs to be removed than with a standard bit. This is the reason that diamond-tipped core drills are commonly used in construction to create holes for pipes, manholes, and other large-diameter penetrations in concrete or stone.
Core drills are used frequently in mineral exploration where the coring may be several hundred to several thousand feet in length. The core samples are recovered and examined by geologists for mineral percentages and stratigraphic contact points. This gives exploration companies the information necessary to begin or abandon mining operations in a particular area.
Before the start of World War Two, Branner Newsom, a California mining engineer, invented a core drill that could take out large diameter cores up to 16 feet in length for mining shafts. This type of core drill is no longer in use as modern drill technology allows standard drilling to accomplish the same at a much cheaper cost.
Core drills come with several power choices including electric, pneumatic, hydraulic (all of which require power sources, such as a generator).
HOW TO CUT CONCRETE
Concrete is usually cut with diamond blades. There are different solutions to perform concrete cutting under different circumstances.
If the job is of shallow cutting and small scale, In this case, you can use a 4″ or 5″ angle grinder, and a 4″ or 5″ sintered diamond blade, for example, segmented diamond blade,turbo diamond blade, or turbo wave diamond blade, mounted on the grinder. Segmented diamond blades may cause more chips during the cutting due to their segmented rim, but they are cheaper. Turbo wave diamond blades can be used to perform higher load tasks for their strengthened steel core, but their price is the highest in these 3 kinds of sintered diamond blades.
You can first cut the concrete to 1/4″ deep, and see how the angle grinder and the diamond blade respond. If no problem, you can do further passes of cuttings to reach the depth of the cut you need. Each cutting pass should not be deeper than 1/2″.
To reduce the dust, you can ask someone to spray some water onto the diamond blade and the cut during the cutting process. This can also help to cool the diamond blade and extend its life. If it is not safe to use water for the electric power source of your angle grinder, you should cut the concrete dry. As dry cutting uses the air as the coolant, after a period of cutting you should release the pressure on the diamond blade and allow it to rotate freely to let the air cool it. The period can be a few minutes to a few seconds depending on the hardness of the concrete being cut (the harder the concrete, the shorter the cutting period should be).
Throughout the cutting process, you should wear a professional respirator, for the dust can seriously hurt your health.
In addition to angle grinder, you can use a circular saw to do the job. Circular saws have a baseplate which can help to keep the cut straight and uniform. With a circular saw, you can also use a bigger diamond blade, e.g., 7″, to improve the cutting efficiency, for circular saws are stabler.
If the job is of deep cutting or big scale
If your cutting is deeper than 4″ (about 100mm) or the job scale is fairly big, you should use a wet concrete saw and laser welded diamond concrete saw blades to do the job. The concrete saw can be a handheld cut-off saw, a walk behind saw, or another type. The diameter of the laser welded diamond blade is usually no smaller than 12″ (300mm). The concrete saw and the diamond blades can be either bought or rented. To obtain good cutting result and improve cutting efficiency, you can follow below steps to prepare the concrete cutting:
1. Identify what concrete you will cut
There are many types of concrete, and they should be cut with different types of diamond blades.
Some concrete has steel bars (reinforced concrete). If your cutting depth is about 4″ or deeper, you may meet the steel bars halfway. There are diamond blades specially for cutting reinforced concrete.
The curing time of concrete varies. Fresh (green) concrete is more abrasive, and old (cured) concrete is harder. Diamond blades for cutting green concrete and cured concrete are also designed to be different.
If possible, you can further investigate the aggregate and the sand of the concrete, for these information can help you to choose the more suitable diamond blades. Hard aggregate like basalt and quartz dulls the diamonds on the blade faster, so the blade’s bond should be softer to let new diamonds be exposed more easily. The size of the aggregate also affects how hard the blade’s bond should be. Small aggregate (smaller than 3/8″) wears the blade faster than big aggregate (bigger than 3/4″). The type of the sand affects the concrete’s abrasiveness. Sharp sand such as crushed sand and river bank sand is more abrasive than round sand like river sand.
2. Choose the proper diamond blades
Though silver brazed diamond blades were used widely in wet concrete cutting before, now laser welded diamond blades are more common for their firm laser weld and high performance.
You should check what diameters of diamond blades your concrete saw can accommodate, and the saw’s arbor size which the arbor hole on the diamond blade should match. Also, you should examine the horsepower of the concrete saw. The saw’s horsepower affects the diamond blade selecting. Diamond blades used on big horsepower saws should have harder bond or higher diamond concentration, otherwise the blade may be consumed very quickly.
Then, you can tell the diamond blade’s diameter and arbor hole size, the horsepower of your concrete saw, along with all the detailed information of the concrete you get in the first step to your diamond blade supplier. The supplier should know which kind of diamond blade may fit your job.
3. Determine wet cutting or dry cutting
Concrete is usually cut with water (wet cutting), for cutting concrete with adequate water can significantly reduce the dust, keep the diamond blade cool and extend its life, and improve the cutting efficiency (for wet cutting can be deep and continuous).
However, when there is no water source near the work area, you have to perform dry cutting. As said in the previous section, dry cutting should be intermittent and shallow. If deep cutting is needed, you should do several passes of shallow cuttings.
4. Wear enough personal protective equipment
You should at least wear a professional respirator, not only in dry cutting, but also in wet cutting, because the small dust particles generated in the concrete cutting process can penetrate deep into the lungs and can cause serious health effects such as lung cancer or silicosis. If the job is big, other equipment like goggle, earplugs, and protective clothing should also be adopted.
5. Pre-cut a shallow straight line on the concrete
To make the cut straight, you can use a chalk line to mark a straight line on the concrete, and then place a straight wood board along the line. Then you can cut a shallow line on the concrete along the wood board. The cut can be about 1/4″ deep.
Having this shallow straight cut, you can perform further cuttings along it to gain the cut you need.
More tips for concrete cutting
Concrete can also be cut with abrasive blades, but diamond blades are recommended, for diamond blades can provide at least two times faster cutting, less downtime, and constant depth of cuts.
If you use the diamond blades occasionally and your jobs are small, you can choose the economical grade diamond blades to save your expense (but the cutting speed of the economical diamond blades should be fast enough). If you use the diamond blades frequently or the job is big, you should choose high grade professional diamond blades, for this can decrease your cost per cut.